> Do you like to say that the Mashey shell also used the string stack and a 
> SIGSEV handler?
Don't think it did: http://www.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s2/sh.c

> Well, from a talk from Stephen Bourne I know that both the Bourne Shell and the 
> Mashey shell did start as a modified Thompson shell. I should have a look at the
> Thompson shell sources…
Also did not: http://www.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/s2/sh.c